Design and thermal evaluation of soluble polyazomethines based on 1,1-Bis[4-(4-benzaldehyde oxy)phenyl]cyclohexane

Introduction

Polyazomethines are a class of polymers containing -CH = Nfunctional repeat units in the main polymer backbone. The aromatic azomethine linkage in polymer backbone is of special interest due to syn / antiisomerism which has an effect on the thermal and photochromic properties. Aromatic polyazomethines exhibit good thermal stability and environmental resistance [1][2][3][4][5][6][7][8][9][10][11][12] . The -CH = Nlinkage in polyazomethines is isoelectronics with -C = Cgroup and therefore finds applications in optoelectronics [13][14][15][16][17][18][19][20][21][22] . The first polymer of this class was synthesized by Adams et al. by polycondensation reaction between terephthalaldehyde and benzidine. In 1950 Marvel and Hill synthesized polyazomethines by solution polycondensation of aromatic dialdehydes with o-phenylene diamine, polyazomethines have high strength and high modulus [23][24][25][26][27][28] .

Experimental 2.1 Materials

4-(P)fluorobenzaldehyde (spectrochem) was used as received, potassium carbonate was dried in oven at 150 o C for 6 hours. Isopropyl alcohol (2-Proponol) was purified by distillation. DMAc was purified before use as described in chapter -2 various commercial diamines (make-aldrich) were used as received LiCl was dried under oven at 150 o C for 6 hours.

Synthesis of Monomer a) Synthesis of 1.1bis (4hydroxy phenyl) cyclohexane -BHPC (II)

In 500ml round bottom flask equipped with thermowell, condenser and magnetic stirrer were placed 47 gm (0.5 mol) of phenol and 24.5 g (0.25 mol) of cyclohexanone. To this solution 100 mL of conc. 36% HCl and 50 mL of glacial acetic acid were added. Resulting reaction mixture was stirred for 5 hours at 45 o C and overnight at room temperature. The pink colour product was isolated by filtration and washed with hot water till it is free from phenol and acid and then with benzene. A crude bisphenol (BHPC) was purified by dissolving in minimum quantity of 2M NaOH at room temperature and the resulting solution was filtered to remove the gummy product the filtrate was acidified with conc. HCl to yield the product. The product was filtered washed with water till acid free and dried. Finally the bisphenol was recrystallized from methanol get white shining crystals.  Yield: 21.83 gm (91%)  M.P.:188-190 °C 2.3. Polymer Synthesis:-By using the aromatic dialdehyde monomer 1,1bis [4 -(4'benzaldehyde oxy) phenyl] cyclohexane BBPC (III) with various commercial diamines. Series of poly (etherazomethine)s were prepared by solution polycondensation method is given below.

Synthesis of polyazomethine (PAM-1) from 1,1[4-(4benzaldehyde oxy) phenyl] cyclohexane, (BBPC) and 4, 4'sulphonyldianiline (SDA) diamine

In 100 mL three necked round bottom flask equipped with magnetic stirrer, calcium chloride guard tube, nitogen gas inlet were placed the 4, 4'sulphonyldianiline (SDA) diamine 0.248 g 1 mmol and dry distilled N, N dimethyl acetamide DMAc 3 mL containing 5% (0.150 g) dry LiCl mixture was stirred at room temperature to get the solution and then dialdehyde 1, 1bis [4 -(4benzaldehyde oxy) phenyl] cyclohexane -BBPC (III) (0.476 g 1 mmol) was added. The reaction mixture was stirred overnight at room temperature. Finally, the mixture was stirred for four hours at 140 o C temperature. Then the solution was cooled to room temperature and poured in 200 mL water with rapid stirring the precipitated polymer (PAM-1) was filtered, washed with water, ethanol and dried in vacuum oven at 80 o C temperature for 6 hours.  Yield = 93% Other polyazomethines PAM-2 to PAM-5 were synthesized with similar procedure by using different diamines.

Results and Discussion

Polyazomethines, also known as polyimines or Schiff's base polymers exhibit good thermal stability and environmental resistance and they are promising materials in optoelectronic and photonic applications. A remarkable characteristic of polyazomethines is their tendancy to increase in molecular weight and crystallinity upon thermal annealing a process that usually brings about as improvement in the mechanical properties of derived fibers. Melt polymerization techniques resulted in infusible materials which cannot be further fabricated into thin film or remoulded. To increase the molecular weight of the products various attempts were made by changing solvent catalyst, temperature, dehydrating agent etc. (the degree of polymerization ranged from 3 to 8 as calculated by nitrogen analysis for these polyazomethines) It is generally recognized that an aryl ether linkage imparts properties such as better solubility and melt processing characteristics and improved toughness in comparison with those of the polymers without an arylether linkage. ----------DCM ----------H2SO4 + + + + + + + + + + + +: Soluble, --: Insoluble Thermal behavior of polymers (PAM) was evaluated by thermogravimetric and differential scanning calorimetry under nitrogen atmosphere. (Table 3) Incorporate the thermal data such as glass transition temperature (Tg), initial decomposition temperature (Ti), 10% weight loss temperature (T10) maximum decomposition temperature (Tmax) and residual weight at 900 °C. TGA curves (Fig. 4) of all poly(ether-azomethine)s showed more or less similar pattern of decomposition with no weight loss below 199°C. The Ti and T10 of these polyazomethines varied in the range 199 to 214 °C and 421 to 607 °C respectively. Tmax values were between 619 to 661 °C and the char yield at 900 °C were in the range 32 to 42 °C. This showed that, these polyazomethines exhibited good thermal stability. Poly(ether-azomethine)s were also characterized by wide angle X-Ray diffractograms-WAXD. The X-Ray diffraction pattern of all Poly(ether-azomethine)s are shown in (Fig. 6).

FT-IR Reports Instrumentation

It was observed that, polyazomethines exhibited partly crystalline to amorphous nature peeks observed in the range 2θ = 10 to 30 °.

Conclusions

A novel aromatic dialdehyde monomer, 1,1[4-(4benzaldehyde oxy)phenyl]cyclohexane (BBPC), containing an ether linkage, was synthesized. Various aromatic diamines featuring methylene, ether, and sulphonyl linkages were also prepared for the synthesis of aromatic polyazomethines. The structure of the monomer was confirmed using FT-IR, spectroscopy. Aromatic poly(ether-azomethine)s were synthesized by the solution polycondensation method, involving a stoichiometric reaction between the novel aromatic dialdehyde (BBPC) and the aromatic diamines. The resulting polyazomethines were characterized using a variety of techniques including FT-IR spectroscopy, inherent viscosity measurements, solubility tests, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and X-ray Diffraction (XRD). The inherent viscosities of the synthesized poly(etherranged from 0.22 to 0.45 dL/g, indicating a moderate molecular weight build-up in these polymers. Solubility tests revealed that the polyazomethines were soluble in aprotic polar solvents such as DMAc, DMSO, DMF, NMP, as well as in m-cresol and pyridine. The glass transition temperatures (Tg) of the polyazomethines synthesized from BBPC and the diamines were found to be in the range of 154°C to 187°C.Thermal stability of the polymers, evaluated by TGA under a nitrogen atmosphere, showed that the polyazomethines possessed excellent thermal resistance, with no significant weight loss at high temperatures.

References

1. Yang CJ, Jenekhe SA. Macromolecules. 1995;28:1130.
2. D'Alelio GF. In: Encyclopedia of Polymer Science and Engineering. 1st ed. Vol. 10. New York: John Wiley and Sons; 1969. p. 659.
3. Cotten RJ, Matzner M. Org Chem (N Y). 1972;13B:1.
4. D'Alelio GF, Crivello JV, Schoenig RK, Huemmer TF. J Macromol Sci Chem. 1967;1:1161.
5. Morgan PW, Kowlek SL, Pletcher TC. Macromolecules. 1987;20:729.
6. Marvel CS, Hill HW. J Am Chem Soc. 1950;72:4819.
7. Marvel CS, Bonsignore PV. J Am Chem Soc. 1959;81:2668.
8. Adams R, Bullock RE, Willson WC. J Am Chem Soc. 1923;45:521.
9. Morgan PW, Pletcher TC, Kwolek SL. Polym Prepr. 1983;24:470.
10. Imai Y, Maldar NN, Kakimoto M. J Polym Sci Polym Chem. 1984;22:3771.
11. Wojtkowski PW. Macromolecules. 1987;20:740.
12. Yang HH. Aromatic High-Strength Fibers. New York: Wiley-Interscience; 1989. p. 641.
13. Yeakel C, Gower K, Mani RS, Allen RD, Mohanty DK. Makromol Chem. 1993;194:2779.
14. Jenekhe SA, Yang CJ, Vanherzeele H, Meth JS. Chem Mater. 1991;3:985.
15. Yang CJ, Jenekhe SA, Meth JS, Vanherzeele H. Mater Res Soc Symp Proc. 1992;247:247.
16. Yang CJ, Jenekhe SA. Chem Mater. 1994;6:196.
17. Mohite SS, Wadgaonkar PP. Polym Prepr. 1990;31:482.
18. Catanescu O, Grigoras M, Colotin G, Dobreanu A, Hurduc N, Simionescu CI. Eur Polym J. 2001;37:2213.
19. McElvain J, Tatsuura S, Wudl F, Heeger A. Synth Met. 1998;95:101.
20. Dutta PK, Jain P, Sen P, Trivedi R, Sen PK, Dutta J. Eur Polym J. 2003;39:1007.
21. Ribera D, Mantecón A, Serra A. J Polym Sci Polym Chem. 2002;40:4344.
22. Smith OD, Holzberlein RL, McGrath JE. Polym Mater Sci Eng. 1989;60.
23. Patel JR, Patel MN. J Macromol Sci Chem. 1989;5:817.
24. Gopal J, Srinivasan M. J Polym Sci. 1986;24:2789.
25. Yang CJ, Jenekhe SA. Chem Mater. 1991;3:878.
26. Saeguss Y, Koshikowa T, Nakamura S. J Polym Sci. 1992;30:1369-1375.
27. Banerjee S, Cutch PK, Saxena C. J Polym Sci Polym Chem. 1995;33:1719.